Resist composition and patterning process

ABSTRACT

A polymer capable of increasing alkali solubility under the action of acid, as a base resin is blended with a copolymer comprising recurring units derived from acenaphthylene, indene, benzofuran or benzothiophene and fluorine-containing recurring units, as a polymeric additive to formulate a resist composition. The photoresist film formed using the resist composition is effective for minimizing outgassing therefrom during the EUV lithography. The resist film has a hydrophilic surface and is effective for suppressing formation of blob defects after development.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2012-194741 filed in Japan on Sep. 5, 2012,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a resist composition, especially chemicallyamplified positive resist composition, comprising a polymer comprisingrecurring units having an acid labile group in blend with a copolymercomprising recurring units derived from a monomer selected fromacenaphthylene, indene, benzofuran, and benzothiophene and recurringunits having fluorine, and a patterning process using the same.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, extreme ultraviolet (EUV)lithography of 13.5 nm wavelength, and double patterning version of theArF lithography, on which active research efforts have been made.

With respect to high-energy radiation of very short wavelength such aselectron beam (EB) or x-ray, hydrocarbons and similar light elementsused in resist materials have little absorption. Then polyhydroxystyrenebase resist materials are under consideration. Resist materials for EBlithography are practically used in the mask image writing application.Recently, the mask manufacturing technology becomes of greater interest.Reduction projection exposure systems or steppers have been used sincethe time when the exposure light was g-line. While their demagnificationfactor was ⅕, a factor of ¼ is now used as a result of chip sizeenlargement and projection lens diameter increase. It becomes of concernthat a dimensional error of a mask has an impact on the dimensionalvariation of a pattern on wafer. It is pointed out that as the patternfeature is reduced, the value of a dimensional variation on the waferbecomes greater than the value of a dimensional error of the mask. Thisis evaluated by a mask error enhancement factor (MEEF) which is adimensional variation on wafer divided by a dimensional error of mask.Patterns on the order of 45 nm often show an MEEF in excess of 4. In asituation including a demagnification factor of ¼ and a MEEF of 4, themask manufacture needs an accuracy substantially equivalent to that forequi-magnification masks.

The exposure system for mask manufacturing made a transition from thelaser beam exposure system to the EB exposure system to increase theaccuracy of line width. Since a further size reduction becomes possibleby increasing the accelerating voltage of the electron gun in the EBexposure system, the accelerating voltage increased from 10 keV to 30keV and reached 50 keV in the current mainstream system, with a voltageof 100 keV being under investigation.

As the accelerating voltage increases, a lowering of sensitivity ofresist film becomes of concern. As the accelerating voltage increases,the influence of forward scattering in a resist film becomes so reducedthat the contrast of electron image writing energy is improved toameliorate resolution and dimensional control whereas electrons can passstraightforward through the resist film so that the resist film becomesless sensitive. Since the mask exposure tool is designed for exposure bydirect continuous writing, a lowering of sensitivity of resist filmleads to an undesirably reduced throughput. Due to a need for highersensitivity, chemically amplified resist compositions are contemplated.

Thinning of resist film is in progress to facilitate reduction ofpattern feature in the EB lithography for mask manufacturing and toprevent the pattern from collapsing due to a higher aspect ratio duringdevelopment. In the case of photolithography, a thinning of resist filmgreatly contributes to resolution improvement. This is becauseintroduction of chemical mechanical polishing (CMP) or the like hasdriven forward device planarization. In the case of mask manufacture,substrates are flat, and the thickness of processable substrates (e.g.,Cr, MoSi or SiO₂) is predetermined by a percent light shield or phaseshift control. The dry etch resistance of resist film must be improvedbefore the film can be reduced in thickness.

It is generally believed that there is a correlation between the carbondensity and the dry etch resistance of resist film. For EB writing whichis not affected by absorption, resist materials based on novolac resinshaving better etch resistance have been developed. Indene copolymersdescribed in Patent Document 1 and acenaphthylene copolymers describedin Patent Document 2 are expected to have improved etch resistance dueto a high carbon density and a robust main chain structure based oncycloolefin structure.

Also, with respect to the soft x-ray (EUV) lithography at wavelength5-20 nm, the reduced absorption of carbon atoms was reported. Increasingthe carbon density is effective not only for improving dry etchresistance, but also for increasing the transmittance in the soft x-raywavelength region.

As the feature size is reduced, image blurs due to acid diffusion becomea problem. To insure resolution for fine patterns with a size of 45 nmet seq., not only an improvement in dissolution contrast is requisite,but control of acid diffusion is also important, as known from previousreports. Since chemically amplified resist compositions are designedsuch that sensitivity and contrast are enhanced by acid diffusion, anattempt to minimize acid diffusion by reducing the temperature and/ortime of post-exposure baking (PEB) fails, resulting in drasticreductions of sensitivity and contrast. Since the distance of aciddiffusion is closely related to the type of acid labile group, it wouldbe desirable to have an acid labile group which permits deprotectionreaction to proceed at a very short distance of acid diffusion.

A tradeoff among sensitivity, edge roughness and resolution is reported.Increasing sensitivity leads to reductions of edge roughness andresolution. Controlling acid diffusion improves resolution at thesacrifice of edge roughness and sensitivity. Addition of an acidgenerator capable of generating a bulky acid is effective forsuppressing acid diffusion, but leads to reductions of edge roughnessand sensitivity as pointed out above. It is then proposed tocopolymerize a polymer with an acid generator in the form of an oniumsalt having polymerizable olefin. Patent Documents 3 to 5 disclosesulfonium salts having polymerizable olefin capable of generating asulfonic acid and similar iodonium salts. A photoresist using a basepolymer having a polymerizable acid generator copolymerized thereinexhibits reduced edge roughness due to controlled acid diffusion anduniform dispersion of acid generator within the polymer, succeeding inimproving both resolution and edge roughness at the same time.

One problem in the EUV lithography is that outgassing components from aresist film during exposure adsorb to the surface of a reflecting mirrorand mask in the exposure tool to reduce their reflectivity. It isproposed to form a protective film atop the resist film for the purposeof reducing the outgassing. Then, a coater cup is necessary for coatingof the protective film. At the early stage of the immersion lithography,a protective film was applied in order to prevent the acid generatorfrom being leached out of the resist film into water. However, theprovision of a protective film brings about a drop of throughput and arise of material cost. Because of these problems, the protective film isgradually going out of use. Under the circumstances, it would bedesirable to have a resist material for the EUV lithography which caneliminate or reduce outgassing without the aid of protective film.

Patent Documents 6 and 7 disclose resist materials wherein a copolymerof a styrene derivative and a recurring unit having fluorine or acopolymer of vinylnaphthalene and a recurring unit having fluorine isadded to a base polymer. When these resist materials are spin coated,the polymer having styrene units or vinylnaphthalene units segregates ina surface layer of the coating, achieving both water-repellent andanti-reflection effects. The patent documents also refer to thesuppression of outgassing in the EUV lithography. However, the styreneand vinylnaphthalene units achieve insufficient suppression ofoutgassing. There exists a desire to have a resist surface modifyingmaterial capable of effectively shutting off outgassing.

CITATION LIST

-   Patent Document 1: JP 3865048-   Patent Document 2: JP-A 2006-169302-   Patent Document 3: JP-A H04-230645-   Patent Document 4: JP-A 2005-084365-   Patent Document 5: JP-A 2006-045311-   Patent Document 6: JP 4771974-   Patent Document 7: JP 4900603

DISCLOSURE OF INVENTION

An object of the present invention is to provide a resist compositionwhich can minimize outgassing from a resist film and prevent formationof blob defects during the EUV lithography; and a pattern formingprocess using the same.

The inventors have found that a satisfactory resist composition isobtainable by adding a copolymer comprising recurring units derived froma monomer selected from acenaphthylene, indene, benzofuran, andbenzothiophene, and recurring units having at least one fluorine atom toa polymer capable of increasing alkali solubility under the action ofacid.

According to the invention, a fluorochemical surfactant of polymer typecomprising recurring units derived from acenaphthylene or analogue isadded to a polymer or base resin to formulate a resist material. Whenthe resist material is coated, a layer of the recurring units derivedfrom acenaphthylene or analogue is formed on the surface of the resistfilm. This surface layer has a high film density enough to preventoutgassing components from escaping from within the resist film. Inaddition, since the fluorochemical surfactant of polymer type comprisingrecurring units derived from acenaphthylene or analogue dissolves in analkaline developer, it renders the resist surface after exposure anddevelopment more hydrophilic and is thus effective for suppressingformation of blob and bridge defects. By virtue of these advantages, theresist material is best suited as a mask blank resist material havinglong-term stability after coating and stability against exposure invacuum and an EUV resist material featuring minimal outgassing invacuum. A pattern forming process using the resist material is alsoprovided.

In one aspect, the invention provides a resist composition comprising

a polymer capable of increasing alkali solubility under the action ofacid, as a base resin and

a copolymer comprising recurring units derived from at least one monomerselected from the group consisting of acenaphthylene, indene,benzofuran, and benzothiophene, and recurring units having at least onefluorine atom, as a polymeric additive.

In a preferred embodiment, the copolymer comprising recurring unitsderived from at least one monomer selected from the group consisting ofacenaphthylene, indene, benzofuran, and benzothiophene, and recurringunits having at least one fluorine atom has the general formula (1).

Herein R¹ and R² each are hydrogen, or C₁-C₄ straight or branched alkyl,alkoxy, acyloxy, hydroxyl, carboxyl, alkoxycarbonyl, or —OC(═O)R,wherein R is a C₁-C₆ straight or branched alkyl or fluoroalkyl group. R³and R⁶ each are hydrogen or methyl. X² is a single bond, —O—,—C(═O)—O—R⁸— or —C(═O)—NH—R⁸—, wherein R⁸ is a single bond or a C₁-C₄straight or branched alkylene group which may contain an ester or ethermoiety. The subscript n is 1 or 2. In case of n=1, X¹ is a single bond,—O—, —C(═O)—O—R⁸— or —C(═O)—NH—R⁸—, wherein R⁸ is a single bond or aC₁-C₄ straight or branched alkylene group which may be substituted withfluorine and which may contain an ester or ether moiety. In case of n=2,X¹ is —C(═O)—O—R⁹═ or —C(═O)—NH—R⁹═, wherein R⁹ is a trivalent groupobtained by eliminating one hydrogen from a C₁-C₁₀ straight, branched orcyclic alkylene group, which may be substituted with fluorine and whichmay contain an ester or ether moiety. R⁴ is a C₁-C₁₂ straight, branchedor cyclic alkylene group, phenylene group, or a combination of alkylenewith phenylene, which may be substituted with fluorine and which maycontain an ester or ether moiety. R⁵ is hydrogen, fluorine, methyl,trifluoromethyl or difluoromethyl, or R⁵ may bond with R⁴ to form a ringwhich may have an ether, fluorinated alkylene or trifluoromethyl moiety.R⁷ is a C₁-C₂₀ straight, branched or cyclic alkyl group which issubstituted with at least one fluorine atom and which may contain anether, ester or sulfonamide moiety. M is a methylene group, oxygen atomor sulfur atom. Subscripts p-1, p-2, q-1 and q-2 are numbers in therange: 0 (p-1)<1.0, 0≦(p-2)<1.0, 0<(p-1)+(p-2)<1.0, 0≦(q-1)<1.0,0≦(q-2)<1.0, 0<(q-1)+(q-2)<1.0, and 0.5≦(p-1)+(p-2)+(q-1)+(q-2)≦1.0.

Typically, the resist composition is a chemically amplified positiveresist composition.

In a preferred embodiment, the polymer serving as a base resin comprisesrecurring units having an acid labile group and recurring units having ahydroxyl group and/or lactone ring as an adhesive group

In a more preferred embodiment, the polymer serving as a base resincomprises recurring units of at least one type selected from recurringunits (a1) and (a2) having a carboxyl and/or phenolic hydroxyl groupwhose hydrogen atom is substituted by an acid labile group, asrepresented by the general formula (2), and recurring units having aphenolic hydroxyl group and/or lactone ring as an adhesive group and hasa weight average molecular weight of 1,000 to 500,000.

Herein R¹⁰ and R¹² are each independently hydrogen or methyl, R¹¹ andR¹³ each are an acid labile group, Y¹ is a single bond, a C₁-C₁₂ linkinggroup having at least one of ester, lactone ring, phenylene andnaphthylene, a phenylene group or a naphthylene group, Y² is a singlebond, ester group or amide group, subscripts a1 and a2 are numbers inthe range: 0≦a1≦0.9, 0≦a2≦0.9, and 0<a1+a2<1.0.

In a further preferred embodiment, the polymer comprising recurringunits of at least one type selected from recurring units (a1) and (a2)having a carboxyl and/or phenolic hydroxyl group whose hydrogen atom issubstituted by an acid labile group, represented by the general formula(2), has further copolymerized therein recurring units of at least onetype selected from sulfonium salt units (b1) to (b3), as represented bythe general formula (3).

Herein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl, R⁰²¹ is asingle bond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, Y is oxygen or NH,R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylenegroup or phenylene group, which may contain a carbonyl (—CO—), ester(—COO—), ether (—O—), or hydroxyl moiety, R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶, R⁰²⁷,R⁰²⁹, R⁰³⁰, and R⁰³¹ are each independently a straight, branched orcyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester or ethermoiety, a C₆-C₁₂ aryl group, a C₇-C₂₀ aralkyl group, or a thiophenylgroup, Z¹ is a single bond, methylene, ethylene, phenylene, fluorinatedphenylene, —O—R⁰³²—, or —C(═O)—Z²—R⁰³²—, Z² is oxygen or NH, R⁰³² is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene group orphenylene group, which may contain a carbonyl, ester, ether or hydroxylmoiety, M⁻ is a non-nucleophilic counter ion, subscripts b1, b2 and b3are numbers in the range: 0≦b1≦0.3, 0≦b2≦0.3, 0≦b3≦0.3, and0<b1+b2+b3≦0.3.

The resist composition may further comprise at least one of an organicsolvent, basic compound, dissolution regulator, and surfactant.

In another aspect, the invention provides a pattern forming processcomprising the steps of applying the resist composition defined aboveonto a substrate to form a coating, baking, exposing the coating tohigh-energy radiation, and developing the exposed coating in adeveloper.

The high-energy radiation is typically KrF excimer laser of wavelength248 nm, ArF excimer laser of wavelength 193 nm, electron beam or softx-ray of wavelength 3 to 15 nm.

Advantageous Effects of Invention

The photoresist film formed using the resist composition of theinvention is effective for minimizing the emission of outgassingcomponents from the resist film during the EUV lithography. Since theresist film has a hydrophilic surface, it is effective for suppressingformation of blob defects after development.

DESCRIPTION OF EMBODIMENTS

The singular forms “a,” “an” and “the” include plural referents unlessthe context clearly dictates otherwise. “Optional” or “optionally” meansthat the subsequently described event or circumstances may or may notoccur, and that description includes instances where the event orcircumstance occurs and instances where it does not.

As used herein, the terminology “(meth)acrylic acid” or “(meth)acrylate”refers collectively to acrylic and methacrylic acid or acrylate andmethacrylate. The terminology “C_(x)-C_(y)”, as applied to a particularunit, such as, for example, a chemical compound or a chemicalsubstituent group, means having a carbon atom content of from “x” carbonatoms to “y” carbon atoms per such unit.

The abbreviations have the following meaning.

EB: electron beamEUV: extreme ultravioletPAG: photoacid generatorPEB: post-exposure bakeLER: line edge roughnessLWR: line width roughnessMw: weight average molecular weightMn: number average molecular weightMw/Mn: dispersity or average molecular weight distributionGPC: gel permeation chromatography

Making efforts to overcome the outstanding problems, the inventors havefound that a resist composition obtained by blending an ordinary basepolymer which turns alkali soluble under the action of acid with acopolymer comprising recurring units derived from a monomer selectedfrom among acenaphthylene, indene, benzofuran, and benzothiophene andrecurring units having at least one fluorine atom is effective forsuppressing the emission of outgassing components from the resist filmduring exposure in vacuum by the EUV lithography. Because of theirrobustness and high density, acenaphthylene and indene derivatives areeffective for shutting off outgassing from the photoresist film. Sincethe copolymer has fluorine-containing recurring units copolymerizedtherein, it will segregate on the surface of the resist film after spincoating.

Polymeric Additive

One embodiment of the invention is a resist composition comprising apolymer capable of increasing alkali solubility under the action ofacid, serving as a base resin, and a copolymer comprising recurringunits derived from at least one monomer selected from amongacenaphthylene, indene, benzofuran, and benzothiophene, and recurringunits having at least one fluorine atom, serving as a polymericadditive. Typically, the copolymer has the general formula (1).

Herein R¹ and R² each are hydrogen, or C₁-C₄ straight or branched alkyl,alkoxy, acyloxy, hydroxyl, carboxyl, alkoxycarbonyl, or —OC(═O)R,wherein R is a C₁-C₆ straight or branched alkyl or fluoroalkyl group. R³and R⁶ each are hydrogen or methyl. X² is a single bond, —O—,—C(═O)—O—R⁸— or —C(═O)—NH—R⁸—, wherein R⁸ is a single bond or a C₁-C₄straight or branched alkylene group which may contain an ester or ethermoiety. The subscript n is 1 or 2. In case of n=1, X¹ is a single bond,—O—, —C(═O)—O—R⁸— or —C(═O)—NH—R⁸—, wherein R⁸ is a single bond or aC₁-C₄ straight or branched alkylene group which may be substituted withfluorine and which may contain an ester or ether moiety. In case of n=2,X¹ is —C(═O)—O—R⁹═ or —C(═O)—NH—R⁹═, wherein R⁹ is a trivalent groupobtained by eliminating one hydrogen from a C₁-C₁₀ straight, branched orcyclic alkylene group, which may be substituted with fluorine and whichmay contain an ester or ether moiety. R⁴ is a C₁-C₁₂ straight, branchedor cyclic alkylene group, phenylene group, or a combination of alkylenewith phenylene, which may be substituted with fluorine and which maycontain an ester or ether moiety. R⁵ is hydrogen, fluorine, methyl,trifluoromethyl or difluoromethyl, or R⁵ may bond with R⁴ to form a ringwhich may have an ether, fluorinated alkylene or trifluoromethyl moiety.R⁷ is a C₁-C₂₀ straight, branched or cyclic alkyl group which issubstituted with at least one fluorine atom and which may contain anether, ester or sulfonamide moiety. M is a methylene group, oxygen atomor sulfur atom, subscripts p-1, p-2, q-1 and q-2 are numbers in therange: 0≦(p-1)<1.0, 0≦(p-2)<1.0, 0<(p-1)+(p-2)<1.0, 0≦(q-1)<1.0,0≦(q-2)<1.0, 0<(q-1)+(q-2)<1.0, and 0.5≦(p-1)+(p-2)+(q-1)+(q-2)≦1.0.

The resist composition having the copolymer comprising recurring unitsof formula (1) added thereto is coated to form a photoresist film. Thephotoresist film is characterized in that a polymeric surfactant havingcopolymerized therein recurring units derived from at least one monomerselected from among acenaphthylene, indene, benzofuran, andbenzothiophene and recurring units having a fluoroalkyl group is presenton the film surface. The polymeric surfactant segregates on thephotoresist film surface at the end of photoresist coating and functionsto suppress the release of outgassing components from the resist filmand to minimize defects in the resist pattern after development.

While the recurring units derived from at least one monomer selectedfrom among acenaphthylene, indene, benzofuran, and benzothiophene arerepresented by units (p-1) and (p-2) in formula (1), examples of themonomers from which units (p-1) and (p-2) are derived are shown below,but not limited thereto.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetyl, acetal or similar group at the monomer stage,and the polymerization be followed by deprotection reaction to restorethe hydroxyl group. Where the hydroxyl group is replaced by an acetylgroup, the polymerization may be followed by alkaline hydrolysis todeprotect the acetyl group into a hydroxyl group. Where the hydroxylgroup is replaced by an acid labile group such as acetal, deprotectionvia hydrolysis with an acid catalyst may be carried out to restore ahydroxyl group.

The recurring units having fluorine are typically recurring units (q-1)having an α-trifluoromethyl alcohol group and recurring units (q-2)having a fluoroalkyl group in formula (1).

Examples of the monomer from which recurring units (q-1) having anα-trifluoromethyl alcohol group are derived are given below.

Note that R³ is as defined above.

Examples of the monomer from which recurring units (q-2) having afluoroalkyl group are derived are given below.

Note that R⁶ is as defined above.

In addition to the recurring units (p-1), (p-2), (q-1) and (q-2) informula (1), the copolymer to be added to the resist composition mayhave further copolymerized therein recurring units (r) having a carboxylgroup for the purposes of improving alkali solubility and rendering theresist film after development more hydrophilic.

Examples of the recurring units (r) having a carboxyl group are givenbelow.

While the copolymer to be added to the resist composition as polymericadditive comprises the recurring units (p-1), (p-2), (q-1) and (q-2) andoptionally, the recurring units (r), their molar fraction is in thefollowing range:

0≦(p-1)<1.0, 0≦(p-2)<1.0, 0<(p-1)+(p-2)<1.0, preferably 0≦(p-1)≦0.9,0≦(p-2)≦0.9, 0.02≦(p-1)+(p-2)≦0.9, and more preferably 0≦(p-1)≦0.8,0≦(p-2)≦0.8, 0.04≦(p-1)+(p-2)≦0.8;0≦(q-1)<1.0, 0≦(q-2)<1.0, 0<(q-1)+(q-2)<1.0, and0.5≦(p-1)+(p-2)+(q-1)+(q-2)≦1.0;0≦r<1.0, preferably 0≦r≦0.8, more preferably 0≦r≦0.7;provided that (p-1)+(p-2)+(q-1)+(q-2)+r=1.0.

Base Resin

The polymer serving as a base resin in the resist composition of theinvention essentially comprises recurring units having an acid labilegroup. Specifically, the recurring units having an acid labile groupinclude recurring units (a1) of (meth)acrylate having an acid labilegroup R¹¹ substituted thereon and recurring units (a2) of hydroxystyrenehaving an acid labile group R¹³ substituted thereon, as represented bythe general formula (2).

Herein R¹⁰ and R¹² are each independently hydrogen or methyl, R¹¹ andR¹³ each are an acid labile group, Y¹ is a single bond, a C₁-C₁₂ linkinggroup having at least one of ester, lactone ring, phenylene andnaphthylene, a phenylene group or a naphthylene group, Y² is a singlebond, ester group or amide group, subscripts a1 and a2 are numbers inthe range: 0≦a1≦0.9, 0≦a2≦0.9, and 0<a1+a2<1.0.

Examples of the monomer from which recurring units (a1) are derived aregiven below.

Note that R¹⁰ and R¹¹ are as defined above.

Examples of the monomer from which recurring units (a2) are derived aregiven below.

Note that R¹² and R¹³ are as defined above.

The acid labile groups represented by R¹¹ and R¹³ in formula (2) may beselected from a variety of such groups. The acid labile groups may bethe same or different and preferably include groups of the followingformulae (A-1) to (A-3).

In formula (A-1), R^(L30) is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in whicheach alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (A-3). Exemplary tertiary alkylgroups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxolan-5-yl. Letter A1 is an integer of 0 to 6.

In formula (A-2), R^(L31) and R^(L32) are hydrogen or straight, branchedor cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms. Exemplary alkyl groups include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl,2-ethylhexyl, and n-octyl. R^(L33) is a monovalent hydrocarbon group of1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may containa heteroatom such as oxygen, examples of which include straight,branched or cyclic alkyl groups and substituted forms of such alkylgroups in which some hydrogen atoms are replaced by hydroxyl, alkoxy,oxo, amino, alkylamino or the like. Illustrative examples of thesubstituted alkyl groups are shown below.

A pair of R^(L31) and R^(L32), R^(L31) and R^(L33), or R^(L32) andR^(L33) may bond together to form a ring with the carbon and oxygenatoms to which they are attached. Each of R^(L31), R^(L32) and R^(L33)is a straight or branched alkylene group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms when they form a ring, while the ringpreferably has 3 to 10 carbon atoms, more preferably 4 to 10 carbonatoms.

Examples of the acid labile groups of formula (A-1) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl groups.

Also included are substituent groups having the formulae (A-1)-1 to(A-1)-10.

Herein R^(L37) is each independently a straight, branched or cyclicC₁-C₁₀ alkyl group or C₆-C₂₀ aryl group. R^(L38) is hydrogen or astraight, branched or cyclic C₁-C₁₀ alkyl group. R^(L39) is eachindependently a straight, branched or cyclic C₂-C₁₀ alkyl group orC₆-C₂₀ aryl group. A1 is an integer of 0 to 6.

Of the acid labile groups of formula (A-2), the straight and branchedones are exemplified by the following groups having formulae (A-2)-1 to(A-2)-35.

Of the acid labile groups of formula (A-2), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Other examples of acid labile groups include those of the followingformula (A-2a) or (A-2b) while the polymer may be crosslinked within themolecule or between molecules with these acid labile groups.

Herein R^(L40) and R^(L41) each are hydrogen or a straight, branched orcyclic C₁-C₈ alkyl group, or R^(L40) and R^(L41), taken together, mayform a ring with the carbon atom to which they are attached, and R^(L40)and R^(L41) are straight or branched C₁-C₈ alkylene groups when theyform a ring. R^(L42) is a straight, branched or cyclic C₁-C₁₀ alkylenegroup. Each of B1 and D1 is 0 or an integer of 1 to 10, preferably 0 oran integer of 1 to 5, and C1 is an integer of 1 to 7. “A” is a(C1+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group having 1 to 50 carbonatoms, which may be separated by a heteroatom or in which some hydrogenatoms attached to carbon atoms may be substituted by hydroxyl, carboxyl,carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or —NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkyltriyl and alkyltetrayl groups,and C₆-C₃₀ arylene groups, which may contain a heteroatom or in whichsome hydrogen atoms attached to carbon atoms may be substituted byhydroxyl, carboxyl, acyl groups or halogen atoms. The subscript C1 ispreferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (A-2a) and (A-2b) areexemplified by the following formulae (A-2)-36 through (A-2)-43.

In formula (A-3), R^(L34), R^(L35) and R^(L36) each are a monovalenthydrocarbon group, typically a straight, branched or cyclic C₁-C₂₀ alkylgroup, which may contain a heteroatom such as oxygen, sulfur, nitrogenor fluorine. A pair of R^(L34) and R^(L35), R^(L34) and R^(L36), orR^(L35) and R^(L36) may bond together to form a C₃-C₂₀ ring with thecarbon atom to which they are attached.

Exemplary tertiary alkyl groups of formula (A-3) include tert-butyl,triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, andtert-amyl.

Other exemplary tertiary alkyl groups include those of the followingformulae (A-3)-1 to (A-3)-18.

Herein R^(L43) is each independently a straight, branched or cyclicC₁-C₈ alkyl group or C₆-C₂₀ aryl group, typically phenyl or naphthyl,R^(L44) and R^(L46) each are hydrogen or a straight, branched or cyclicC₁-C₂₀ alkyl group, and R^(L45) is a C₆-C₂₀ aryl group, typicallyphenyl.

The polymer may be crosslinked within the molecule or between moleculeswith groups having R^(L47) which is a di- or multi-valent alkylene orarylene group, as shown by the following formulae (A-3)-19 and (A-3)-20.

Herein R^(L43) is as defined above, R^(L47) is a straight, branched orcyclic C₁-C₂₀ alkylene group or arylene group, typically phenylene,which may contain a heteroatom such as oxygen, sulfur or nitrogen, andE1 is an integer of 1 to 3.

Of recurring units having acid labile groups of formula (A-3), recurringunits of (meth)acrylate having an exo-form structure represented by theformula (A-3)-21 are preferred.

Herein, R¹⁰ is as defined above. R^(c3) is a straight, branched orcyclic C₁-C₈ alkyl group or an optionally substituted C₆-C₂₀ aryl group.R^(c4) to R^(c9), R^(c12) and R^(c13) are each independently hydrogen ora monovalent C₁-C₁₅ hydrocarbon group which may contain a heteroatom.R^(c10) and R^(c11) each are hydrogen or a monovalent C₁-C₁₅ hydrocarbongroup which may contain a heteroatom. Alternatively, a pair of R^(c4)and R^(c5), R^(c6) and R^(c8), R^(c6) and R^(c9), R^(c7) and R^(c9),R^(c7) and R^(c13), R^(c8) and R^(c12), R^(c10) and R^(c11), or R^(c11)and R^(c12), taken together, may form a ring, and in that event, eachring-forming R is a divalent C₁-C₁₅ hydrocarbon group which may containa heteroatom. Also, a pair of R^(c4) and R^(c13), R^(c10) and R^(c13),or R^(c6) and R^(c8) which are attached to vicinal carbon atoms may bondtogether directly to form a double bond. The formula also represents anenantiomer.

The ester form monomers from which recurring units having an exo-formstructure represented by formula (A-3)-21 are derived are described inU.S. Pat. No. 6,448,420 (JP-A 2000-327633). Illustrative non-limitingexamples of suitable monomers are given below.

Also included in the acid labile groups of formula (A-3) are acid labilegroups of (meth)acrylate having furandiyl, tetrahydrofurandiyl oroxanorbornanediyl as represented by the following formula (A-3)-22.

Herein, R¹⁰ is as defined above. R^(c14) and R^(c15) are eachindependently a monovalent, straight, branched or cyclic C₁-C₁₀hydrocarbon group, or R^(c14) and R^(c15), taken together, may form analiphatic hydrocarbon ring with the carbon atom to which they areattached. R^(c16) is a divalent group selected from furandiyl,tetrahydrofurandiyl and oxanorbornanediyl. R^(c17) is hydrogen or amonovalent, straight, branched or cyclic C₁-C₁₀ hydrocarbon group whichmay contain a heteroatom.

Examples of the monomers from which the recurring units substituted withacid labile groups having furandiyl, tetrahydrofurandiyl andoxanorbornanediyl are derived are shown below. Note that Me is methyland Ac is acetyl.

In a preferred embodiment of the polymer serving as base resin,recurring units (c) having an adhesive group may be copolymerized withthe recurring units (a1) and (a2) having an acid labile group,represented by formula (2), for the purposes of improving compatibilitywith other components and suppressing a film thickness loss on theresist surface. Suitable adhesive groups include hydroxyl, carboxyl,lactone ring, carbonyl, carbonate, ester, ether, amide, sulfonamide,cyano, sulfonic acid ester, lactam and the like. The preferred recurringunits (c) are those having a phenolic hydroxyl group which has asensitizing effect in the EB and EUV lithography. The recurring units(c) having a phenolic hydroxyl group are typically selected from units(c1) to (c9) represented by the general formula (4).

Herein R²¹ is each independently hydrogen or methyl, V¹, V² and V⁵ eachare a single bond or —C(═O)—O—R²³—, V³ and V⁴ each are —C(═O)—O—R²⁴—,R²³ and R²⁴ each are a single bond or a straight, branched or cyclicC₁-C₁₀ alkylene group which may contain an ether or ester moiety, R²² iseach independently hydrogen, or a C₁-C₄ straight or branched alkyl,alkoxy, cyano, alkoxycarbonyl, acyloxy or acyl group, W¹ and W² each aremethylene or ethylene, W³ is methylene, oxygen or sulfur, W⁴ and W⁵ eachare CH or nitrogen, and s and t each are 1 or 2.

Examples of the monomers from which the recurring units (c1) to (c9)having a phenolic hydroxyl group are derived are given below.

Examples of the monomers from which the recurring units having anadhesive group such as hydroxyl (exclusive of phenolic hydroxyl),lactone ring, ether, ester, carbonyl, cyano, sulfonic acid ester,sulfonamide group, cyclic —O—C(═O)—S— or —O—C(═O)—NH— group are derivedare given below.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxy group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

In a more preferred embodiment, the polymer serving as base resin hasfurther copolymerized therein recurring units (d) selected from units(d1) to (d5) of indene, acenaphthylene, chromone, coumarin, andnorbornadiene, or derivatives thereof, represented by the followingformula (5).

Herein R²⁵ is each independently hydrogen, a C₁-C₃₀ alkyl, haloalkyl,alkoxy, alkanoyl or alkoxycarbonyl group, C₆-C₁₀ aryl group, halogen, or1,1,1,3,3,3-hexafluoro-2-propanol group, and W⁶ is methylene, oxygen orsulfur. As used herein, the term “haloalkyl” refers to alkyl in whichsome or all hydrogen atoms are substituted by halogen.

Examples of suitable monomers from which recurring units (d1) to (d5) ofindene, acenaphthylene, chromone, coumarin, and norbornadienederivatives are derived are given below.

In a further embodiment, an acid generator (b) in the form of an oniumsalt having polymerizable olefin may be copolymerized with the foregoingmonomers. JP-A H04-230645, JP-A 2005-084365, and JP-A 2006-045311disclose sulfonium salts having polymerizable olefin capable ofgenerating a specific sulfonic acid and similar iodonium salts. JP-A2006-178317 discloses a sulfonium salt having sulfonic acid directlyattached to the main chain.

In this embodiment, the polymer may have further copolymerized thereinrecurring units (b1) to (b3) having a sulfonium salt, represented by thefollowing formula (3). Sometimes, units (b1) to (b3) are collectivelyreferred to as units (b).

Herein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl. R⁰²¹ is asingle bond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, wherein Y is oxygenor NH, and R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene or phenylene group, which may contain a carbonyl (—CO—),ester (—COO—), ether (—O—) or hydroxyl moiety. R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶,R⁰²⁷, R⁰²⁹, R⁰³⁰, and R⁰³¹ are each independently a straight, branchedor cyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester orether moiety, or a C₆-C₁₂ aryl, C₇-C₂₀ aralkyl, or thiophenyl group. Z¹is a single bond, methylene, ethylene, phenylene, fluorophenylene,—O—R⁰³²—, or —C(═O)—Z²—R⁰³²—, wherein Z² is oxygen or NH, and R⁰³² is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene orphenylene group, which may contain a carbonyl, ester, ether or hydroxylmoiety. M⁻ is a non-nucleophilic counter ion. Molar fractions b1, b2 andb3 are in the range of 0≦b1≦0.3, 0≦b2≦0.3, 0≦b3≦0.3, and 0≦b1+b2+b3≦0.3.

Examples of the non-nucleophilic counter ion represented by M⁻ includehalide ions such as chloride and bromide ions; fluoroalkylsulfonate ionssuch as triflate, 1,1,1-trifluoroethanesulfonate, andnonafluorobutanesulfonate; arylsulfonate ions such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate, and1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such asmesylate and butanesulfonate; imidates such asbis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide andbis(perfluorobutylsulfonyl)imide; methidates such astris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

The attachment of an acid generator to the polymer main chain iseffective in restraining acid diffusion, thereby preventing a reductionof resolution due to blur by acid diffusion. Also edge roughness (LER orLWR) is improved since the acid generator is uniformly dispersed.

In the polymer, recurring units (a) to (d) may be incorporated in thefollowing molar fraction:

0≦a1≦0.9, 0≦a2≦0.9, 0<a1+a2<1.0, preferably 0≦a1≦0.8, 0≦a2≦0.8,0.1≦a1+a2≦0.8, and more preferably 0≦a1≦0.7, 0≦a2≦0.7, 0.2≦a1+a2≦0.7;0≦b1≦0.3, 0≦b2≦0.3, 0≦b3≦0.3, and 0≦b (=b1+b2+b3)≦0.3;0≦c<1.0, preferably 0≦c≦0.9, and more preferably 0≦c≦0.8;0≦d≦0.5, preferably 0≦d≦0.4, and more preferably 0≦d≦0.3;0.5≦a1+a2+b1+b2+b3+c≦1.0, preferably 0.6≦a1+a2+b1+b2+b3+c≦1.0, morepreferably 0.7≦a1+a2+b1+b2+b3+c≦1.0; and a1+a2+b1+b2+b3+c+d=1.

The meaning of a+b+c=1, for example, is that in a polymer comprisingrecurring units (a), (b), and (c), the sum of recurring units (a), (b),and (c) is 100 mol % based on the total amount of entire recurringunits. The meaning of a+b+c<1 is that the sum of recurring units (a),(b), and (c) is less than 100 mol % based on the total amount of entirerecurring units, indicating the inclusion of other recurring units.

There have been described a copolymer of formula (1) as polymericadditive for modifying the resist film surface and an acid labilegroup-containing polymer of formula (2) as base resin. These polymersmay be synthesized by any desired methods, for example, by dissolvingone or more monomers selected from the monomers to form recurring units(p), (q) and (r) or recurring units (a) to (d) in an organic solvent,adding a radical polymerization initiator thereto, and effecting heatpolymerization.

Examples of the organic solvent which can be used for polymerizationinclude toluene, benzene, tetrahydrofuran, diethyl ether and dioxane.Examples of the polymerization initiator used herein include2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

When hydroxyacenaphthylene is copolymerized, an alternative method ispossible. Specifically, acetoxyacenaphthylene is used instead ofhydroxyacenaphthylene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis as mentioned above, for therebyconverting the polymer product to hydroxypolyacenaphthylene. Foralkaline hydrolysis, a base such as aqueous ammonia or triethylamine maybe used. The reaction temperature is −20° C. to 100° C., preferably 0°C. to 60° C., and the reaction time is 0.2 to 100 hours, preferably 0.5to 20 hours.

The polymer, which may be either the copolymer as polymeric additive orthe polymer as base resin, should preferably have a weight averagemolecular weight (Mw) in the range of 1,000 to 500,000, and morepreferably 2,000 to 30,000, as measured by GPC versus polystyrenestandards. With too low a Mw, the resist composition may become lessheat resistant. A polymer with too high a Mw may lose alkalinesolubility and give rise to a footing phenomenon after patternformation.

If a multi-component polymer has a wide molecular weight distribution ordispersity (Mw/Mn), which indicates the presence of lower and highermolecular weight polymer fractions, there is a possibility that foreignmatter is left on the pattern or the pattern profile is degraded. Theinfluences of molecular weight and dispersity become stronger as thepattern rule becomes finer. Therefore, the multi-component polymershould preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0,especially 1.0 to 1.5, in order to provide a resist composition suitablefor micropatterning to a small feature size.

It is understood that a mixture of two or more polymers which differ incompositional ratio, molecular weight or dispersity is acceptable as thebase resin.

The resist composition is based on a blend of an alkali-solublepolymeric additive or copolymer comprising recurring units (p-1), (p-2),(q-1), (q-2) and (r) which segregates on the resist film surface aftercoating and functions to suppress outgassing from the resist film, toprevent formation of bridge and blob defects, and to minimize LWR, andan acid labile group-containing polymer or base polymer comprisingrecurring units (a1), (a2), (b1), (b2), (b3), (c) and (d) which turnssoluble in alkaline developer under the action of acid. Typically thesurface segregating polymeric additive is blended in an amount of 0.1 to50 parts, preferably 0.2 to 30 parts, and more preferably 0.2 to 20parts by weight per 100 parts by weight of the base polymer. Alsotypically, the surface segregating polymeric additive alone has analkaline dissolution rate of 0.1 to 100,000 nm/s, preferably 1 to 50,000nm/s, and more preferably 10 to 20,000 nm/s.

Resist Composition

The resist composition may include an acid generator in order for thecomposition to function as a chemically amplified positive resistcomposition. Typical of the acid generator used herein is a photoacidgenerator (PAG) capable of generating an acid in response to actiniclight or radiation. It is any compound capable of generating an acidupon exposure to high-energy radiation. Suitable PAGs include sulfoniumsalts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, andoxime-O-sulfonate acid generators. The acid generators may be used aloneor in admixture of two or more. Exemplary acid generators are describedin U.S. Pat. No. 7,537,880 (JP-A 2008-111103, paragraphs [0122] to[0142]). In the embodiment wherein a polymer having recurring units (b)copolymerized therein is used as the base resin, the PAG may be omitted.

The resist composition may further comprise an organic solvent, basiccompound, dissolution regulator, surfactant, and acetylene alcohol,alone or in combination.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144] to [0145] (U.S. Pat. No. 7,537,880).Specifically, exemplary solvents include ketones such as cyclohexanoneand methyl-2-n-amyl ketone; alcohols such as 3-methoxybutanol,3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and1-ethoxy-2-propanol; ethers such as propylene glycol monomethyl ether,ethylene glycol monomethyl ether, propylene glycol monoethyl ether,ethylene glycol monoethyl ether, propylene glycol dimethyl ether, anddiethylene glycol dimethyl ether; esters such as propylene glycolmonomethyl ether acetate (PGMEA), propylene glycol monoethyl etheracetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,tert-butyl propionate, and propylene glycol mono-tert-butyl etheracetate; and lactones such as γ-butyrolactone, and mixtures thereof.

Exemplary basic compounds are described in JP-A 2008-111103, paragraphs[0146] to [0164], for example, primary, secondary and tertiary aminecompounds, specifically amine compounds having a hydroxyl, ether, ester,lactone, cyano or sulfonate group. Exemplary surfactants are describedin JP-A 2008-111103, paragraphs [0165] to [0166]. Exemplary dissolutionregulators are described in JP-A 2008-122932 (US 2008090172), paragraphs[0155] to [0178], and exemplary acetylene alcohols in paragraphs [0179]to [0182]. Also useful are quenchers of polymer type as described inJP-A 2008-239918. The polymeric quencher segregates at the resistsurface after coating and thus enhances the rectangularity of resistpattern. When a protective film is applied as is often the case in theimmersion lithography, the polymeric quencher is also effective forpreventing any film thickness loss of resist pattern or rounding ofpattern top.

An appropriate amount of the acid generator used is 0.01 to 100 parts,and preferably 0.1 to 80 parts. An appropriate amount of the organicsolvent used is 50 to 10,000 parts, especially 100 to 5,000 parts. Thedissolution regulator may be blended in an amount of 0 to 50 parts,preferably 0 to 40 parts, the basic compound in an amount of 0 to 100parts, preferably 0.001 to 50 parts, and the surfactant in an amount of0 to 10 parts, preferably 0.0001 to 5 parts. All amounts are expressedin parts by weight relative to 100 parts by weight of the base resin.

Process

The resist composition, typically chemically amplified positive resistcomposition comprising a polymeric additive of formula (1), an acidlabile group-containing polymer of formula (2), an acid generator, and abasic compound in an organic solvent is used in the fabrication ofvarious integrated circuits. Pattern formation using the resistcomposition may be performed by well-known lithography processes. Theprocess generally involves coating, prebake, exposure, bake (PEB), anddevelopment. If necessary, any additional steps may be added.

The resist composition is first applied onto a substrate on which anintegrated circuit is to be formed (e.g., Si, SiO₂, SiN, SiON, TiN, WSi,BPSG, SOG, or organic antireflective coating) or a substrate on which amask circuit is to be formed (e.g., Cr, CrO, CrON, MoSi, or SiO₂) by asuitable coating technique such as spin coating, roll coating, flowcoating, dip coating, spray coating or doctor coating. The coating isprebaked on a hot plate at a temperature of 60 to 150° C. for 10 secondsto 30 minutes, preferably 80 to 120° C. for 30 seconds to 20 minutes.The resulting resist film is generally 0.1 to 2.0 μm thick.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, x-ray, excimer laser light, γ-ray,synchrotron radiation or EUV (soft x-ray), directly or through a mask.The exposure dose is preferably about 1 to 200 mJ/cm², more preferablyabout 10 to 100 mJ/cm², or 0.1 to 100 μC/cm², more preferably 0.5 to 50μC/cm². The resist film is further baked (PEB) on a hot plate at 60 to150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes.

Thereafter the resist film is developed in a developer in the form of anaqueous base solution for 3 seconds to 3 minutes, preferably 5 secondsto 2 minutes by conventional techniques such as dip, puddle or spraytechniques. Suitable developers are 0.1 to 10 wt %, preferably 2 to 10wt %, more preferably 2 to 8 wt % aqueous solutions oftetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide(TEAH), tetrapropylammonium hydroxide (TPAH) and tetrabutylammoniumhydroxide (TBAH). The resist film in the exposed area is dissolved inthe developer whereas the resist film in the unexposed area is notdissolved. In this way, the desired positive pattern is formed on thesubstrate. It is appreciated that the resist composition of theinvention is best suited for micro-patterning using such high-energyradiation as EB, EUV (soft x-ray), x-ray, γ-ray and synchrotronradiation among others.

Although TMAH aqueous solution is generally used as the developer, TEAH,TPAH and TBAH having a longer alkyl chain are effective in inhibitingthe resist film from being swollen during development and thuspreventing pattern collapse. JP 3429592 describes an example using anaqueous TBAH solution for the development of a polymer comprisingrecurring units having an alicyclic structure such as adamantanemethacrylate and recurring units having an acid labile group such ast-butyl methacrylate, the polymer being water repellent due to theabsence of hydrophilic groups.

The TMAH developer is most often used as 2.38 wt % aqueous solution,which corresponds to 0.26N. The TEAH, TPAH, and TBAH aqueous solutionsshould preferably have an equivalent normality. The concentration ofTEAH, TPAH, and TBAH that corresponds to 0.26N is 3.84 wt %, 5.31 wt %,and 6.78 wt %, respectively.

When a pattern with a line size of 32 nm or less is resolved by the EBand EUV lithography, there arises a phenomenon that lines become wavy,lines merge together, and merged lines collapse. It is believed thatthis phenomenon occurs because lines are swollen in the developer andthe thus expanded lines merge together. Since the swollen linescontaining liquid developer are as soft as sponge, they readily collapseunder the stress of rinsing. For this reason, the developer using along-chain alkyl developing agent is effective for preventing film swelland hence, pattern collapse.

Alternatively, a negative tone pattern may be formed by organic solventdevelopment. The organic solvent used as the developer is preferablyselected from 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone,4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone,methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate,butyl acetate, isobutyl acetate, amyl acetate, isoamyl acetate, butenylacetate, phenyl acetate, propyl formate, butyl formate, isobutylformate, amyl formate, isoamyl formate, methyl valerate, methylpentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethylpropionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate,propyl lactate, butyl lactate, isobutyl lactate, amyl lactate, isoamyllactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methylbenzoate, ethyl benzoate, benzyl acetate, methyl phenylacetate, benzylformate, phenylethyl formate, methyl 3-phenylpropionate, benzylpropionate, ethyl phenylacetate, and 2-phenylethyl acetate. Theseorganic solvents may be used alone or in admixture of two or more.

At the end of organic solvent development, the resist film is rinsed. Asthe rinsing liquid, a solvent which is miscible with the developer anddoes not dissolve the resist film is preferred. Suitable solventsinclude alcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12carbon atoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alkanes of 6 to 12 carbonatoms include hexane, heptane, octane, nonane, decane, undecane,dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-tert-amylether, and di-n-hexyl ether. The solvents may be used alone or inadmixture. Besides the foregoing solvents, aromatic solvents may beused, for example, toluene, xylene, ethylbenzene, isopropylbenzene,tert-butylbenzene and mesitylene.

EXAMPLE

Examples and Comparative Examples are given below for furtherillustrating the invention, but they should not be construed as limitingthe invention thereto. Mw is a weight average molecular weight asmeasured by GPC versus polystyrene standards, and Mw/Mn designatesmolecular weight distribution or dispersity. All parts (pbw) are byweight.

Preparation of Copolymers

Various copolymers (Copolymers 1 to 13) to be added to resistcompositions were prepared by combining suitable monomers, effectingcopolymerization reaction in methyl ethyl ketone solvent, pouring intohexane for crystallization, repeatedly washing with hexane, isolation,and drying. The copolymers were analyzed by ¹H-NMR to determine theircomposition and by GPC to determine Mw and dispersity Mw/Mn.

Copolymer 1

Mw=8,300

Mw/Mn=1.85

Copolymer 2

Mw=8,100

Mw/Mn=1.82

Copolymer 3

Mw=7,200

Mw/Mn=1.69

Copolymer 4

Mw=8,000

Mw/Mn=1.80

Copolymer 5

Mw=8,100

Mw/Mn=1.74

Copolymer 6

Mw=9,200

Mw/Mn=1.84

Copolymer 7

Mw=6,800

Mw/Mn=1.65

Copolymer 8

Mw=6,300

Mw/Mn=1.69

Copolymer 9

Mw=6,800

Mw/Mn=1.65

Copolymer 10

Mw=6,100

Mw/Mn=1.88

Copolymer 11

Mw=6,600

Mw/Mn=1.89

Copolymer 12

Mw=6,300

Mw/Mn=1.93

Copolymer 13

Mw=6,300

Mw/Mn=1.93

Examples and Comparative Examples Preparation of Resist Composition

A positive resist composition in solution form was prepared bydissolving a resist film surface-modifying copolymer (Copolymers 1 to13, shown above), a polymer obtained by conventional radicalpolymerization (Resist Polymers 1 to 5, shown below) and components in asolvent in accordance with the formulation of Table 1 and filteringthrough a filter with a pore size of 0.2 μm.

EUV Lithography Patterning Test

On a silicon substrate having a diameter of 4 inches, asilicon-containing SOG film of SHB-A940 (Shin-Etsu Chemical Co., Ltd.)was formed to a thickness of 35 nm. The positive resist composition wascoated on the SOG film and prebaked on a hot plate at 110° C. for 60seconds to form a resist film of 35 nm thick. The resist film wasexposed to EUV through a pseudo phase-shift-mask (PSM) in an exposuretool (NA 0.3), baked (PEB) at the temperature shown in Table 2,developed in 0.20N tetrabutylammonium hydroxide (TBAH) aqueous solutionfor 30 seconds, rinsed with deionized water, and spin dried, forming aresist pattern. Sensitivity is the dose at which a 20-nm line-and-spacepattern was formed. Maximum resolution is the minimum size which wasresolved at that dose. The pattern was measured for edge roughness (LWR)under SEM. The results are shown in Table 2.

Outgassing Test Simulated for EUV Lithography

The resist composition (see Table 3) was coated onto a HMDS-primed12-inch wafer to form a resist film of 60 nm thick. Using a resistoutgassing tool (EUV Tech), the resist film was exposed to EB in avarying dose, baked (PEB) at the temperature shown in Table 3, anddeveloped in an alkaline developer (2.38 wt % TMAH aqueous solution). E0is the dose at which the film thickness became 0 nm. After the wafer wassubjected to flood exposure at the dose of E0, the thickness ofcontaminants deposited on Witness Plate was measured by spectralellipsometry. The results are shown in Table 3.

Resist Polymer 1

Mw=6,700

Mw/Mn=1.58

Resist Polymer 2

Mw=6,900

Mw/Mn=1.68

Resist Polymer 3

Mw=6,200

Mw/Mn=1.81

Resist Polymer 4

Mw=7,200

Mw/Mn=1.52

Resist Polymer 5

Mw=5,200

Mw/Mn=1.61

TABLE 1 Polymer PAG Quencher Additive Surfactant Solvent (pbw) (pbw)(pbw) (pbw) (pbw) (pbw) Resist 1 Resist — Quencher Copolymer 1 FC-4430PGMEA (2,000) Polymer 1 (1.123) (5.0) (0.001) PGME (1,000) (100) CyH(3,000) Resist 2 Resist — Quencher Copolymer 1 FC-4430 PGMEA (2,000)Polymer 2 (1.123) (5.0) (0.001) PGME (1,000) (100) CyH (3,000) Resist 3Resist — Quencher Copolymer 1 FC-4430 PGMEA (2,000) Polymer 3 (1.123)(5.0) (0.001) PGME (1,000) (100) CyH (3,000) Resist 4 Resist — QuencherCopolymer 1 FC-4430 PGMEA (2,000) Polymer 4 (1.123) (5.0) (0.001) PGME(1,000) (100) CyH (3,000) Resist 5 Resist PAG 1 Quencher Copolymer 1FC-4430 PGMEA (4,000) Polymer 5 (25) (1.123) (5.0) (0.001) CyH (2,000)(100) Resist 6 Resist — Quencher Copolymer 2 FC-4430 PGMEA (2,000)Polymer 1 (1.123) (5.0) (0.001) PGME (1,000) (100) CyH (3,000) Resist 7Resist — Quencher Copolymer 3 FC-4430 PGMEA (2,000) Polymer 1 (1.123)(5.0) (0.001) PGME (1,000) (100) CyH (3,000) Resist 8 Resist — QuencherCopolymer 4 FC-4430 PGMEA (2,000) Polymer 1 (1.123) (5.0) (0.001) PGME(1,000) (100) CyH (3,000) Resist 9 Resist — Quencher Copolymer 5 FC-4430PGMEA (2,000) Polymer 1 (1.123) (5.0) (0.001) PGME (1,000) (100) CyH(3,000) Resist 10 Resist — Quencher Copolymer 6 FC-4430 PGMEA (2,000)Polymer 1 (1.123) (5.0) (0.001) PGME (1,000) (100) CyH (3,000) Resist 11Resist — Quencher Copolymer 7 FC-4430 PGMEA (2,000) Polymer 1 (1.123)(5.0) (0.001) PGME (1,000) (100) CyH (3,000) Resist 12 Resist — QuencherCopolymer 8 FC-4430 PGMEA (2,000) Polymer 1 (1.123) (5.0) (0.001) PGME(1,000) (100) CyH (3,000) Resist 13 Resist — Quencher Copolymer 9FC-4430 PGMEA (2,000) Polymer 1 (1.123) (5.0) (0.001) PGME (1,000) (100)CyH (3,000) Resist 14 Resist — Quencher Copolymer 10 FC-4430 PGMEA(2,000) Polymer 1 (1.123) (5.0) (0.001) PGME (1,000) (100) CyH (3,000)Resist 15 Resist — Quencher Copolymer 11 FC-4430 PGMEA (2,000) Polymer 1(1.123) (5.0) (0.001) PGME (1,000) (100) CyH (3,000) Resist 16 Resist —Quencher Copolymer 12 FC-4430 PGMEA (2,000) Polymer 1 (1.123) (5.0)(0.001) PGME (1,000) (100) CyH (3,000) Resist 17 Resist — QuencherCopolymer 13 FC-4430 PGMEA (2,000) Polymer 1 (1.123) (5.0) (0.001) PGME(1,000) (100) CyH (3,000) Comparative Resist — Quencher — FC-4430 PGMEA(2,000) Resist 1 Polymer 1 (1.123) (0.001) PGME (1,000) (100) CyH(3,000) PGMEA: propylene glycol monomethyl ether acetate PGME: propyleneglycol monomethyl ether CyH: cyclohexanone FC-4430: fluorochemicalsurfactant by 3M-Sumitomo Co., Ltd.

TABLE 2 PEB temp. Sensitivity Maximum resolution LWR (° C.) (mJ/cm²)(nm) (nm) Resist 1 90 15 17 4.0 Resist 2 85 16 18 4.3 Resist 3 85 17 173.9 Resist 4 85 17 17 3.8 Resist 5 85 15 16 5.0 Resist 6 90 15 17 4.2Resist 7 90 15 17 4.3 Resist 8 90 15 17 4.0 Resist 9 90 15 17 4.0 Resist10 90 15 17 4.0 Resist 11 90 15 17 4.1 Resist 12 90 15 17 4.0 Resist 1390 15 17 4.1 Resist 14 90 16 17 4.1 Resist 15 90 17 17 4.2 Resist 16 9015 17 4.3 Resist 17 90 15 17 4.6 Comparative Resist 1 90 15 20 6.0

TABLE 3 PEB temp. (° C.) Contamination thickness (nm) Resist 1 90 1.0Comparative Resist 1 90 2.5

Japanese Patent Application No. 2012-194741 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A resist composition comprising a polymer capable of increasingalkali solubility under the action of acid, as a base resin and acopolymer comprising recurring units derived from at least one monomerselected from the group consisting of acenaphthylene, indene,benzofuran, and benzothiophene, and recurring units having at least onefluorine atom, as a polymeric additive.
 2. The resist composition ofclaim 1 wherein the copolymer has the general formula (1):

wherein R¹ and R² each are hydrogen, or C₁-C₄ straight or branchedalkyl, alkoxy, acyloxy, hydroxyl, carboxyl, alkoxycarbonyl, or —OC(═O)R,wherein R is a C₁-C₆ straight or branched alkyl or fluoroalkyl group, R³and R⁶ each are hydrogen or methyl, X² is a single bond, —O—,—C(═O)—O—R⁸— or —C(═O)—NH—R⁸—, wherein R⁸ is a single bond or a C₁-C₄straight or branched alkylene group which may contain an ester or ethermoiety, n is 1 or 2, in case of n=1, X¹ is a single bond, —O—,—C(═O)—O—R⁸— or —C(═O)—NH—R⁸—, wherein R⁸ is a single bond or a C₁-C₄straight or branched alkylene group which may be substituted withfluorine and which may contain an ester or ether moiety, in case of n=2,X¹ is —C(═O)—O—R⁹═ or —C(═O)—NH—R⁹═, wherein R⁹ is a trivalent groupobtained by eliminating one hydrogen from a C₁-C₁₀ straight, branched orcyclic alkylene group, which may be substituted with fluorine and whichmay contain an ester or ether moiety, R⁴ is a C₁-C₁₂ straight, branchedor cyclic alkylene group, phenylene group, or a combination thereof,which may be substituted with fluorine and which may contain an ester orether moiety, R⁵ is hydrogen, fluorine, methyl, trifluoromethyl ordifluoromethyl, or R⁵ may bond with R⁴ to form a ring which may have anether, fluorinated alkylene or trifluoromethyl moiety, R⁷ is a C₁-C₂₀straight, branched or cyclic alkyl group which is substituted with atleast one fluorine atom and which may contain an ether, ester orsulfonamide moiety, M is a methylene group, oxygen atom or sulfur atom,subscripts p-1, p-2, q-1 and q-2 are numbers in the range: 0≦(p-1)<1.0,0≦(p-2)<1.0, 0<(p-1)+(p-2)<1.0, 0≦(q-1)<1.0, 0≦(q-2)<1.0,0<(q-1)+(q-2)<1.0, and 0.5≦(p-1)+(p-2)+(q-1)+(q-2)≦1.0.
 3. The resistcomposition of claim 1 which is a chemically amplified positive resistcomposition.
 4. The resist composition of claim 1 wherein the polymerserving as a base resin comprises recurring units having an acid labilegroup and recurring units having a hydroxyl group and/or lactone ring asan adhesive group.
 5. The resist composition of claim 4 wherein thepolymer serving as a base resin comprises recurring units of at leastone type selected from recurring units (a1) and (a2) having a carboxyland/or phenolic hydroxyl group substituted with an acid labile group, asrepresented by the general formula (2), and recurring units having aphenolic hydroxyl group and/or lactone ring as an adhesive group and hasa weight average molecular weight of 1,000 to 500,000,

wherein R¹⁰ and R¹² are each independently hydrogen or methyl, R¹¹ andR¹³ each are an acid labile group, Y¹ is a single bond, a C₁-C₁₂ linkinggroup having at least one of ester, lactone ring, phenylene andnaphthylene, a phenylene group or a naphthylene group, Y² is a singlebond, ester group or amide group, subscripts a1 and a2 are numbers inthe range: 0≦a1≦0.9, 0≦a2≦0.9, and 0<a1+a2<1.0.
 6. The resistcomposition of claim 5 wherein the polymer comprising recurring units ofat least one type selected from recurring units (a1) and (a2) having acarboxyl and/or phenolic hydroxyl group substituted with an acid labilegroup, represented by the general formula (2), has further copolymerizedtherein recurring units of at least one type selected from sulfoniumsalt units (b1) to (b3), as represented by the general formula (3),

wherein R⁰²⁰, R⁰²⁴, and R⁰²⁸ each are hydrogen or methyl, R⁰²¹ is asingle bond, phenylene, —O—R⁰³³—, or —C(═O)—Y—R⁰³³—, Y is oxygen or NH,R⁰³³ is a straight, branched or cyclic C₁-C₆ alkylene group, alkenylenegroup or phenylene group, which may contain a carbonyl (—CO—), ester(—COO—), ether (—O—), or hydroxyl moiety, R⁰²², R⁰²³, R⁰²⁵, R⁰²⁶, R⁰²⁷,R⁰²⁹, R⁰³⁰, and R⁰³¹ are each independently a straight, branched orcyclic C₁-C₁₂ alkyl group which may contain a carbonyl, ester or ethermoiety, a C₆-C₁₂ aryl group, a C₇-C₂₀ aralkyl group, or a thiophenylgroup, Z¹ is a single bond, methylene, ethylene, phenylene, fluorinatedphenylene, —O—R⁰³²—, or —C(═O)—Z²—R⁰³²—, Z² is oxygen or NH, R⁰³² is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene group orphenylene group, which may contain a carbonyl, ester, ether or hydroxylmoiety, M⁻ is a non-nucleophilic counter ion, subscripts b1, b2 and b3are numbers in the range: 0≦b1≦0.3, 0≦b2≦0.3, 0≦b3≦0.3, and0<b1+b2+b3≦0.3.
 7. The resist composition of claim 1, further comprisingat least one of an organic solvent, basic compound, dissolutionregulator, and surfactant.
 8. A pattern forming process comprising thesteps of applying the resist composition of claim 1 onto a substrate toform a coating, baking, exposing the coating to high-energy radiation,and developing the exposed coating in a developer.
 9. The process ofclaim 8 wherein the high-energy radiation is KrF excimer laser ofwavelength 248 nm, ArF excimer laser of wavelength 193 nm, electron beamor soft x-ray of wavelength 3 to 15 nm.